2. Field of the Invention
The present invention concerns angular velocity sensors and more particularly angular velocity sensors providing a fluid signal in response to an angular velocity input.
3. Description of the Prior Art
Angular velocity sensors typically produce a signal indicative of the rate at which an object under investigation is spinning. Fluidic angular velocity sensors produce a fluid signal, typically involving fluid pressure or current flow, indicative of the rate of rotation of a rotary input. Angular velocity sensors have a number of widespread applications. One common application concerns anti-locking mechanisms for vehicle brake control systems. The tires of automobiles, motorcycles and other vehicles typically slip slightly with respect to a road surface just before brake lock-up occurs. During this slippage, the time rate of change of the angular velocity of the tire, called angular acceleration, rises significantly. By monitoring this angular acceleration, brake lock-up can be avoided by briefly interrupting the braking force at or near the point of tire slippage, just before the onset of brake lock-up.
While several different types of electronic angular velocity sensors have been developed, numerous applications exist in high radiation, electromagnetic interference and other severe environments in which a fluidic angular velocity sensor would be more dependable than an electronic sensor. The severe conditions in proximity to a vehicle wheel, for example, militate towards use of a fluidic rather than an electronic type of angular velocity sensor. Fluidic angular velocity sensors have been developed in the past, two examples being disclosed in U.S. Pat. Nos. 3,942,557 and 3,347,103. Both of these fluidic sensors, however, require a pressurized fluid source and incorporate an angular velocity dependent fluid restrictive element. U.S. Pat. No. 3,942,557, for example, discloses an angular velocity sensor coupled to a pressurized fluid reservoir. A perforated cup-shaped rotor is disposed within the sensor and coupled to a rotary input. The flow of pressurized fluid past the cup-shaped rotor and consequently the output fluid pressure from the sensor is dependent upon the angular velocity of this rotor. Systems of this sort are not desirable in some applications, such as those in which size and weight are a consideration, since a pressurized fluid reservoir and fluid pressurizing source are generally required. Thus, there still exists a need for a less complex fluidic angular velocity sensor which does not require a pressurized fluid source or reservoir.
Some efforts have previously been made to incorporate a fluid pump into an angular velocity sensor to obviate the need for a pressurized fluid source or reservoir. Fluid pumps, however, typically produce periodic pressure fluxuations at the pump output usually resulting from the action of fluid displacing elements disposed within the pump in proximity to the pump output. These pressure fluctuations have thus far generally precluded the successful incorporation of fluid pumps into an angular velocity sensor. Thus, there still exists a need for a fluidic angular velocity sensor which does not require a pressurized fluid source and has a stable fluid signal output.